Planète Terre : des dangers annoncés

Le changement climatique global est aujourd’hui une réalité, et des indications toujours plus nombreuses montrent qu’il est largement dû aux activités humaines. C’est parce que la communauté scientifique s’est organisée, depuis plusieurs décennies, pour développer un diagnostic étayé, et le relayer auprès du grand public ou des décideurs, qu’une véritable prise de conscience des enjeux de cette évolution a pu se développer

Some Atmospheric Processes Governing the Large-Scale Tropical Circulation in Idealized Aquaplanet Simulations

International audienceThe large-scale tropical atmospheric circulation is analyzed in idealized aquaplanet simulations using an atmospheric general circulation model. Idealized sea surface temperatures (SSTs) are used as lower-boundary conditions to provoke modifications of the atmospheric general circulation. Results show that 1) an increase in the meridional SST gradients of the tropical region drastically strengthens the Hadley circulation intensity, 2) the presence of equatorial zonal SST anomalies weakens the Hadley cells and reinforces the Walker circulation, and 3) a uniform SST warming causes small and nonsystematic changes of the Hadley and Walker circulations. In all simulations, the jet streams strengthen and move equatorward as the Hadley cells strengthen and become narrower.Some relevant mechanisms are then proposed to interpret the large range of behaviors obtained from the simulations. First, the zonal momentum transport by transient and stationary eddies is shown to modulate the eddy-driven jets, which causes the poleward displacements of the jet streams. Second, it is found that the Hadley circulation adjusts to the changes of the poleward moist static energy flux and gross moist static stability, associated with the geographical distribution of convection and midlatitude eddies. The Walker circulation intensity corresponds to the zonal moist static energy transport induced by the zonal anomalies of the turbulent fluxes and radiative cooling. These experiments provide some hints to understand a few robust changes of the atmospheric circulation simulated by ocean–atmosphere coupled models for future and past climates

Some Atmospheric Processes Governing the Large-Scale Tropical Circulation in Idealized Aquaplanet Simulations

International audienceThe large-scale tropical atmospheric circulation is analyzed in idealized aquaplanet simulations using an atmospheric general circulation model. Idealized sea surface temperatures (SSTs) are used as lower-boundary conditions to provoke modifications of the atmospheric general circulation. Results show that 1) an increase in the meridional SST gradients of the tropical region drastically strengthens the Hadley circulation intensity, 2) the presence of equatorial zonal SST anomalies weakens the Hadley cells and reinforces the Walker circulation, and 3) a uniform SST warming causes small and nonsystematic changes of the Hadley and Walker circulations. In all simulations, the jet streams strengthen and move equatorward as the Hadley cells strengthen and become narrower.Some relevant mechanisms are then proposed to interpret the large range of behaviors obtained from the simulations. First, the zonal momentum transport by transient and stationary eddies is shown to modulate the eddy-driven jets, which causes the poleward displacements of the jet streams. Second, it is found that the Hadley circulation adjusts to the changes of the poleward moist static energy flux and gross moist static stability, associated with the geographical distribution of convection and midlatitude eddies. The Walker circulation intensity corresponds to the zonal moist static energy transport induced by the zonal anomalies of the turbulent fluxes and radiative cooling. These experiments provide some hints to understand a few robust changes of the atmospheric circulation simulated by ocean–atmosphere coupled models for future and past climates

Impacts of greenhouse gases and aerosol direct and indirect effects on clouds and radiation in atmospheric GCM simulations of the 1930-1989 period

Among anthropogenic perturbations of the Earth\''s atmosphere, greenhouse gases and aerosols are considered to have a major impact on the energy budget through their impact on radiative fluxes. We use three ensembles of simulations with the LMDZ general circulation model to investigate the radiative impacts of five species of greenhouse gases (CO2, CH4, N2O, CFC-11 and CFC-12) and sulfate aerosols for the period 1930-1989. Since our focus is on the atmospheric changes in clouds and radiation from greenhouse gases and aerosols, we prescribed sea surface temperatures in these simulations. Besides the direct impact on radiation through the greenhouse effect and scattering of sunlight by aerosols, strong radiative impacts of both perturbations through changes in cloudiness are analysed. The increase in greenhouse gas concentration leads to a reduction of clouds at all atmospheric levels, thus decreasing the total greenhouse effect in the longwave spectrum and increasing absorption of solar radiation by reduction of cloud albedo. Increasing anthropogenic aerosol burden results in a decrease in high-level cloud cover through a cooling of the atmosphere, and an increase in the low-level cloud cover through the second aerosol indirect effect. The trend in low-level cloud lifetime due to aerosols is quantified to 0.5 min day-1 decade-1 for the simulation period. The different changes in high (decrease) and low-level (increase) cloudiness due to the response of cloud processes to aerosols impact shortwave radiation in a contrariwise manner, and the net effect is slightly positive. The total aerosol effect including also the aerosol direct and first indirect effects remains strongly negative

A randomized trial comparing adjuvant chemotherapy with gemcitabine plus cisplatin with docetaxel plus cisplatin in patients with completely resected non-small-cell lung cancer with quality of life as the primary objective

International audienceOBJECTIVES: Adjuvant chemotherapy with vinorelbine plus cisplatin (VC) improves survival in resected non-small-cell lung cancer (NSCLC), but has negative impact on quality of life (QoL). In advanced NSCLC, gemcitabine plus cisplatin (GC) and docetaxel plus cisplatin (DC) exhibit comparable efficacy, with possibly superior QoL compared to VC. This trial investigated these regimens in the adjuvant setting. METHODS: Patients with Stage IB to III NSCLC were eligible following standardized surgery. Overall, 136 patients were included, with 67 and 69 assigned to the GC and DC arms, respectively. Cisplatin (75 mg/m(2), Day [D] 1) plus gemcitabine (1250 mg/m(2), D1 and D8) or docetaxel (75 mg/m(2) D1) were administered for three cycles. Primary end-point was QoL (EORTC QLQ-C30), with the study designed to detect a 10-point difference between arms. Overall survival, safety and cost were secondary end-points. RESULTS: No between-group imbalance was observed in terms of patient characteristics. At inclusion, global health status (GHS) scores (/100) were 63.5 and 62.7 in GC and DC, respectively (P = 0.8), improving to 64.5 and 65.4 after 3 months (P = 0.8). No significant difference in functional or symptoms scores was observed between the arms except for alopecia. Grade 3/4 haematological and non-haematological toxicities were found in 33.8 and 21.7% (P = 0.11), and 33.8 and 26.1% (P = 0.33) of patients, in GC and DC, respectively. At 2 years, 92.9 and 89.8% of patients remained alive in GC and DC, respectively (P = 0.88). CONCLUSIONS: DC and GC adjuvant chemotherapies for completely resected NSCLC were well tolerated and appear free of major QoL effects, and are therefore representing candidates for comparison with the standard VC regimen

L'initiative européenne "Suivi global pour l'environnement et la sécurité'' et le protocole de Kyoto

International audienceEn 1992 la Convention Cadre des Nations Unies pour le Contrôle du Changement du Climat (UNFCCC) a montré la prise de conscience internationale des effets néfastes de l'accumulation dans l'atmosphère des gaz à effet de serre, conduisant à un réchauffement climatique, sous l'effet direct ou indirect des activités anthropiques. Le Protocole de Kyoto, adopté en 1997, a fixé des engagements quantitatifs que les parties signataires s'engageaient à respecter. Ceci suppose des moyens d'observation afin de comprendre, modéliser, mesurer l'évolution des sources et des puits de gaz à effet de serre, et tout particulièrement celles sur lesquelles l'Homme peut avoir une influence directe. Conjointement aux mesures in situ, l'observation de la Terre par satellite s'avère un moyen puissant pour répondre à cet objectif. L'Europe, comme le rappelle le "Manifeste de Baveno" adopté par un certain nombre d'agences impliquées dans les activités spatiales, dispose d'atouts majeurs pour remplir de tels objectifs. Le présent article s'efforce de donner une vue synthétique des différentes informations à rassembler pour le suivi des clauses du Protocole de Kyoto, de l'UNFCCC et de leurs conséquences globales sur le changement climatique, mettant en évidence les résultats obtenus, les moyens à entreprendre, les recherches restant à mener, pour atteindre ces buts

The INDC counter, aggregation of national contributrions and 2°C trajectories

Rapport du groupe interdisciplinaire sur les contributions nationalesConsidering that limiting global warming to below 2°C implies a CO2 budget not to be exceeded and near-zero emissions by 21OO (IPCC), we can assess global 2030 greenhouse gas emissions implied by INDCs in comparison to long-term trajectories. Ahead of the COP21, we estimate that submitted INDCs would bring global greenhouse gas emissions in the range of 55 to 64 GtC02eq in 2030.Under this assumption,global emissions in 2030 are thus higher than the level of 51GtC0 2eq for the year 2012. However, this is not in contradiction with a peaking of global emissions that can only be expected after 2020, given in particular the projected dynamics of emissions in China and other developing countries.The published INDCs represent a significant step towards trajectories compatible with the 2°C goal,but remain insufficient to join trajectories presenting a reasonable probability of success.ln order to increase the chance of meeting the 2°C objective, the ambition of the short-term contributions needs to be strengthened in future negotiations.ln order to sustain a high pace in emissions reductions after 2030,structural measures are also needed, which, in order to have a rapi impact, should be prepared as early as possible. Continued efforts are needed to accelerate the development of low carbon solutions on the one hand,and demonstrate the feasibility of negative emissions on the other hand

An Earth-system prediction initiative for the twenty-first century

International audienceSome scientists have proposed the Earth-System Prediction Initiative (EPI) at the 2007 GEO Summit in Cape Town, South Africa. EPI will draw upon coordination between international programs for Earth system observations, prediction, and warning, such as the WCRP, WWRP, GCOS, and hence contribute to GEO and the GEOSS. It will link with international organizations, such as the International Council for Science (ICSU), Intergovernmental Oceanographic Commission (IOC), UNEP, WMO, and World Health Organization (WHO). The proposed initiative will provide high-resolution climate models that capture the properties of regional high-impact weather events, such as tropical cyclones, heat wave, and sand and dust storms associated within multi-decadal climate projections of climate variability and change. Unprecedented international collaboration and goodwill are necessary for the success of EPI